Commit a7c8d58c authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman

tty: Fix unsafe vt paste_selection()

Convert the tty_buffer_flush() exclusion mechanism to a
public interface - tty_buffer_lock/unlock_exclusive() - and use
the interface to safely write the paste selection to the line
discipline.
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 47aa658a
......@@ -29,6 +29,42 @@
#define TTYB_MEM_LIMIT 65536
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* tty_buffer_unlock_exclusive - release exclusive access
*
* @port - tty_port owning the flip buffer
*
* Guarantees safe use of the line discipline's receive_buf() method by
* excluding the buffer work and any pending flush from using the flip
* buffer. Data can continue to be added concurrently to the flip buffer
* from the driver side.
*
* On release, the buffer work is restarted if there is data in the
* flip buffer
*/
void tty_buffer_lock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
}
void tty_buffer_unlock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
int restart;
restart = buf->head->commit != buf->head->read;
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
if (restart)
queue_work(system_unbound_wq, &buf->work);
}
/**
* tty_buffer_space_avail - return unused buffer space
* @port - tty_port owning the flip buffer
......@@ -158,7 +194,7 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
* being processed by flush_to_ldisc then we defer the processing
* to that function
*
* Locking: takes flush_mutex to ensure single-threaded flip buffer
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
......@@ -168,16 +204,16 @@ void tty_buffer_flush(struct tty_struct *tty)
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
buf->flushpending = 1;
atomic_inc(&buf->priority);
mutex_lock(&buf->flush_mutex);
mutex_lock(&buf->lock);
while ((next = buf->head->next) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
}
buf->head->read = buf->head->commit;
buf->flushpending = 0;
mutex_unlock(&buf->flush_mutex);
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
/**
......@@ -383,7 +419,7 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
*
* The receive_buf method is single threaded for each tty instance.
*
* Locking: takes flush_mutex to ensure single-threaded flip buffer
* Locking: takes buffer lock to ensure single-threaded flip buffer
* 'consumer'
*/
......@@ -402,14 +438,14 @@ static void flush_to_ldisc(struct work_struct *work)
if (disc == NULL)
return;
mutex_lock(&buf->flush_mutex);
mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
int count;
/* Ldisc or user is trying to flush the buffers. */
if (buf->flushpending)
/* Ldisc or user is trying to gain exclusive access */
if (atomic_read(&buf->priority))
break;
count = head->commit - head->read;
......@@ -426,7 +462,7 @@ static void flush_to_ldisc(struct work_struct *work)
break;
}
mutex_unlock(&buf->flush_mutex);
mutex_unlock(&buf->lock);
tty_ldisc_deref(disc);
}
......@@ -482,13 +518,12 @@ void tty_buffer_init(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
mutex_init(&buf->flush_mutex);
mutex_init(&buf->lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
atomic_set(&buf->memory_used, 0);
buf->flushpending = 0;
atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc);
}
......@@ -24,6 +24,7 @@
#include <linux/selection.h>
#include <linux/tiocl.h>
#include <linux/console.h>
#include <linux/tty_flip.h>
/* Don't take this from <ctype.h>: 011-015 on the screen aren't spaces */
#define isspace(c) ((c) == ' ')
......@@ -346,8 +347,8 @@ int paste_selection(struct tty_struct *tty)
console_unlock();
ld = tty_ldisc_ref_wait(tty);
tty_buffer_lock_exclusive(&vc->port);
/* FIXME: this is completely unsafe */
add_wait_queue(&vc->paste_wait, &wait);
while (sel_buffer && sel_buffer_lth > pasted) {
set_current_state(TASK_INTERRUPTIBLE);
......@@ -363,6 +364,7 @@ int paste_selection(struct tty_struct *tty)
remove_wait_queue(&vc->paste_wait, &wait);
__set_current_state(TASK_RUNNING);
tty_buffer_unlock_exclusive(&vc->port);
tty_ldisc_deref(ld);
return 0;
}
......@@ -67,8 +67,8 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
struct tty_bufhead {
struct tty_buffer *head; /* Queue head */
struct work_struct work;
struct mutex flush_mutex;
unsigned int flushpending:1;
struct mutex lock;
atomic_t priority;
struct tty_buffer sentinel;
struct llist_head free; /* Free queue head */
atomic_t memory_used; /* In-use buffers excluding free list */
......
......@@ -32,4 +32,7 @@ static inline int tty_insert_flip_string(struct tty_port *port,
return tty_insert_flip_string_fixed_flag(port, chars, TTY_NORMAL, size);
}
extern void tty_buffer_lock_exclusive(struct tty_port *port);
extern void tty_buffer_unlock_exclusive(struct tty_port *port);
#endif /* _LINUX_TTY_FLIP_H */
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